module.exports = function(s){
    s = s || '';
    return ('xxxxxxxx' + s + 'xxxx' + s + '4xxx' + s + 'yxxx' + s + 'xxxxxxxxxxxx').replace(/[xy]/g, function(c) {
        var r = Math.random() * 16 | 0,
            v = c == 'x' ? r : (r & 0x3 | 0x8);
        return v.toString(16);
    }).toUpperCase();
}